The present invention relates to a method and apparatus for cutting by electrical discharges an electrode workpiece by means of a longitudinally fed electrode wire, and more particularly the present invention relates to such a method and apparatus wherein the electrode workpiece and the electrode wire are displaced relative to each other not only according to a predetermined cutting path but also according to an oscillatory motion directed transversely to the cutting path.
Cutting a metallic workpiece in a travelling wire EDM apparatus, by means of an electrode wire of a few tenths of a millimeter in diameter, presents many important problems due to the narrowness of the slit cut in the workpiece, more particularly problems relating to eliminating the machining debris from the machining zone and to maintaining the electrode wire straight between the wire support and guide members. Straightness of the electrode wire in the machining zone is difficult to achieve in view of the forces of attraction and repulsion exerted upon the wire in the course of the electrical discharge machining.
In order to partially solve such problems, it is known to oscillate the wire in a direction transverse to the direction of the cutting path, for example as disclosed in U.S. Pat. No. 2,794,110. There results an increase in width of the slit cut in the workpiece, which greatly improves the disposal of the machining debris and decreases the forces of repulsion exerted on the wire. Such a known method which permits up to a certain point to decrease short circuits and to improve the cooling of the wire, presents advantages only for fast cuts providing a rough surface finish. This in turn requires that a second machining operation, a finish machining operation, be effected on the rough machined surface of the workpiece by effecting a second cutting pass at a much lower machining rate. The second machining operation is time consuming and greatly increases the total costs of the machining operation.